1. Field of the Invention
This invention relates to circuit interrupters and, more particularly, to ground fault and/or arc fault current interrupters and, more particularly, to circuit breakers having a mechanism for opening the associated power circuit in the event of a failure of the circuit breaker separable contacts to trip open, such as, for example, a failure in a ground fault and/or arc fault trip circuit.
2. Background Information
In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light industrial applications, overcurrent protection is typically provided by a thermal-magnetic trip device. This trip device typically includes a bimetal strip that is heated and bends in response to a persistent overload condition. The bimetal, in turn, unlatches a spring powered operating mechanism that opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system.
For short circuit protection, an armature, which is attracted by sizable magnetic forces generated in a magnetic core by a short circuit, unlatches, or trips, a circuit breaker operating mechanism. As an example, the magnetic type actuation occurs when the hot line conductor becomes directly connected with ground or neutral, thereby bypassing the load. In many applications, a miniature circuit breaker may also provide ground fault and/or arc fault protection.
Ground fault current interrupter (GFCI) and arc fault current interrupter (AFCI) circuit breakers are well known in the art. Examples of ground fault and arc fault circuit breakers are disclosed in U.S. Pat. Nos. 4,081,852; 5,260,676; 5,293,522; and 5,896,262. In ground fault circuit breakers, an electronic circuit typically detects leakage of current to ground and generates a ground fault trip signal. This trip signal energizes a trip solenoid, which unlatches the operating mechanism, often through deflection of the armature of the thermal-magnetic trip device.
In conventional ground fault circuit breakers, the ground fault detection circuit is powered from the load side of the circuit breaker such that the detection circuit is not powered after the circuit breaker has detected a ground fault and, thus, has tripped. In this manner, the circuit breaker separable contacts are employed as a cut-off switch to remove power to and, thus, protect the ground fault detection circuit.
When a ground fault circuit interrupter (GFCI), arc fault circuit interrupter (AFCI) or wall outlet GFCI/AFCI unit is called upon to trip, the circuit interrupter or outlet unit trips open the separable contacts of the device. For example, the tripping may be started by using a Push to Test button on the front of the unit, by using a remote tester, or because of a real world arc fault or ground fault.
In the event of a failure in the electronic trip circuit, such as a component failure that disables the trip circuit, the circuit breaker can remain energized after the failure. It is desirable to provide a fail-safe mechanism that would open the separable contacts of the breaker in the event of such failure. It is further desirable to provide a mechanism for preventing resetting of the circuit breaker once the separable contacts have been opened as a result of such failure.
It is known to employ a ground fault detection circuit in a hair dryer. In response to a ground fault, an SCR is fired to electrically connect a resistor between line and neutral conductors. In turn, whenever the resistor opens, a plunger is released to open a set of contacts to open the power circuit to the hair dryer.
There have been reports that some circuit breakers and other types of AFCI and/or GFCI devices might not be able to trip open when called upon to trip and, thus, fail to open the separable contacts as required.
There is a need, therefore, for a mechanism to ensure that the power circuit is opened if a ground fault, arc fault, test method or other trip source calls upon the device to trip to an open position.
The present invention meets this need and others and employs a mechanism to open the power circuit of the circuit interrupter and to prevent the circuit interrupter from being reset. In accordance with the invention, a trip circuit includes a resistor, which is energized in response to a trip condition. The resistor has a body, which burns open in response to a failure of the separable contacts to trip open. A means engages the body of the resistor. A means responsive to that means opens the power circuit in response to the body of the resistor burning open. Hence, the device will have to be replaced since the power circuit will become open and require the user to take immediate action.
As one aspect of the invention, a circuit interrupter comprises: a housing; separable contacts; an operating mechanism for opening and closing the separable contacts; a first trip mechanism including a trip circuit having a resistor, which is energized in response to a trip condition, the first trip mechanism cooperating with the operating mechanism to trip open the separable contacts in response to the trip condition, the resistor having a body which burns open in response to a failure of the separable contacts to trip open; and a second trip mechanism engaging the body of the resistor and cooperating with the operating mechanism to trip open the separable contacts in response to the body of the resistor burning open.
The operating mechanism may include a trip latch, and the first trip mechanism may include a solenoid having a coil and a plunger. The trip circuit energizes the coil through the resistor in response to the trip condition. The energized coil normally moves the plunger to engage the trip latch to trip open the separable contacts in response to the trip condition. The body of the resistor burns open in response to the plunger failing to trip open the separable contacts through the trip latch in response to the trip condition.
The second trip mechanism may include a trip member and a spring biasing the trip member toward the trip latch. The body of the resistor normally blocks the trip member, and burns open to release the trip member and trip open the separable contacts through the trip latch in response to the plunger failing to trip open the separable contacts through the trip latch in response to the trip condition.
As another aspect of the invention, a circuit interrupter comprises: a housing; first separable contacts within the housing; an operating mechanism for opening and closing the first separable contacts; a trip circuit including a resistor, which is energized in response to a trip condition, the trip circuit cooperating with the operating mechanism to trip open the first separable contacts in response to the trip condition, the resistor having a body which burns open in response to a failure in the trip circuit; second separable contacts electrically connected in series with the first separable contacts; a movable contact arm having an open position for opening the second separable contacts and having a closed position for closing the second separable contacts, the movable contact arm held in the closed position thereof by the body of the resistor, the movable contact arm being movable to the open position thereof in response to the body of the resistor burning open; and a spring which biases the movable contact arm toward the open position thereof.
The operating mechanism may include a trip latch. The first separable contacts are adapted to receive a line voltage. The trip circuit may include an SCR and a solenoid having a coil and a plunger. The trip circuit energizes the coil with the line voltage through the resistor and the SCR in response to the trip condition. The energized coil normally moves the plunger to engage the trip latch to trip open the separable contacts in response to the trip condition. The body of the resistor burns open in response to the plunger failing to trip open the separable contacts through the trip latch in response to the trip condition.
As a further aspect of the invention, a circuit interrupter comprises: a housing; a line terminal; a load terminal; a power circuit including separable contacts electrically connected between the line terminal and the load terminal; an operating mechanism for opening and closing the separable contacts; a trip circuit including a resistor, which is energized in response to a trip condition, the trip circuit cooperating with the operating mechanism to trip open the separable contacts in response to the trip condition, the resistor having a body which burns open in response to a failure of the separable contacts to trip open; means for engaging the body of the resistor; and means responsive to the means for engaging for opening the power circuit in response to the body of the resistor burning open.